1. Field of the Invention
The present invention relates generally to optical inspection of semiconductor substrates. More particularly, the present invention relates to a template mask which assists in optical inspection within semiconductor substrates of defects such as, but not limited to, oxidation induced stacking faults.
2. Description of the Related Art
In conjunction with the process by which resistors, transistors, diodes and other electrical circuit elements are formed within and/or upon a semiconductor substrate, it is common in the art of integrated circuit fabrication to form directly upon the surface of the semiconductor substrate an oxide layer. Oxide layers formed directly upon semiconductor substrates typically serve either to isolate active regions of the semiconductor substrate or to provide capacitive gate oxide dielectric layers within field effect transistors (FETs). Commonly, although not exclusively, oxide layers formed directly upon semiconductor substrates within integrated circuits are formed through a thermal oxidation method where a portion of the semiconductor substrate is consumed to form within and/or upon the semiconductor substrate an oxide layer.
Although the thermal oxidation method for forming oxide layers upon semiconductor substrates is quite common in the art, the thermal oxidation method for forming oxide layers upon semiconductor substrates is not entirely without problems. In particular, it is known in the art that the thermal oxidation method for forming oxide layers upon semiconductor substrates suffers from the simultaneous formation of oxidation induced stacking faults within portions of the semiconductor substrate above which is desired to form the oxide layer. The mechanism by which oxidation induced stacking faults are formed within semiconductor substrates incident to forming through thermal oxidation methods oxide layers upon those semiconductor substrates is also known in the art. See, for example S. M. Sze, VLSI Technology, McGraw-Hill, 1988, pp. 133-35, wherein it is disclosed that oxidation induced stacking faults are formed when excess silicon atoms present at the silicon-silicon oxide interface incident to forming through a thermal oxidation method an oxide layer upon a semiconductor substrate nucleate at crystalline defects within the semiconductor substrate, thus forming oxidation induced stacking faults.
The presence of oxidation induced stacking faults within silicon semiconductor substrates is sufficiently common such that generalized test methods have been developed for inspecting silicon semiconductor substrates for those oxidation induced stacking faults. A particularly common, although not exclusive, test method is disclosed by the American Society for the Testing of Materials (ASTM) as test method F416-84, the teachings of which are incorporated herein fully by reference. The generalized test methods, including the ASTM F416-84 method, provide for optical microscopic inspection of several test sites upon a silicon semiconductor substrate upon whose surface is formed an oxide layer through a thermal oxidation method. Although the general methods provide a convenient and standardized means for determining oxidation induced stacking fault areal density within silicon semiconductor substrates, generalized optical microscopic inspection methods, such as the ASTM F416-84 method, are not entirely without problems. For example, the general optical microscopic inspection methods suffer from deficiencies including but not limited to: (1) an inability to exactly define the positions and boundaries of the various sample locations upon a silicon semiconductor substrate to be inspected; (2) an inability to adequately focus an optical microscope through the various sample locations upon a semiconductor substrate to be inspected, particularly under the common circumstance where there is no patterning upon the silicon semiconductor substrate; and (3) an inconsistency in defining equivalent fields of view when employing different optical microscopes for inspecting the same semiconductor substrate. Each of these deficiencies provides genuine limitations in efficiently and reproducibly optically inspecting a silicon semiconductor substrate for defects such as oxidation induced stacking faults through standardized test methods, such as the ASTM F416-84 method.
Thus, it is desirable in the art to provide a simple and uniform optical method and apparatus for inspecting silicon semiconductor substrates for defects such as oxidation induced stacking faults, where the method and apparatus avoids the several deficiencies as noted above. It is towards that goal that the present invention is directed.
Methods and apparatus through which various inspections of semiconductor substrates may be efficiently undertaken are disclosed in the art. For example, Sandland et al. in U.S. Pat. No. 4,618,938 disclose an automated semiconductor substrate inspection apparatus which includes a system computer to provide functions including both: (1) data storage; and (2) movement of the semiconductor substrate. In addition, Haga in U.S. Pat. No. 5,233,203 discloses an additional automated semiconductor substrate inspection apparatus through which the field of view of an optical microscope is moved uniformly along the surface of the semiconductor substrate. Finally, Tateiwa in U.S. Pat. No. 5,444,529 discloses a method for inspecting particles on semiconductor substrates where the particles act as condensation nuclei to form water droplets which more efficiently scatter laser light employed in inspection of the semiconductor substrate.
Desirable in the art are additional methods and apparatus through which semiconductor substrates may be inspected for defects such as, but not limited to, oxidation induced stacking faults. Particularly desirable are optical microscopic inspection methods through which the areal density of oxidation induced stacking faults within semiconductor substrates may be determined while simultaneously: (1) easily defining the positions and boundaries of the various sample locations upon a semiconductor substrate to be inspected; (2) easily focusing an optical microscope upon the various sample locations upon a semiconductor substrate to be inspected, even under conditions where there is no patterning upon the semiconductor substrate; and (3) providing consistency in defining equivalent fields of view even when different optical microscopes are employed when inspecting the same semiconductor substrate.